The present invention relates generally to improvements in series connected light strings. More specifically, the present invention relates to techniques for providing a string set of series-connected lamps in which each of the lamps may operate with a shunt circuit.
One of the most common uses of light strings is for decoration and display purposes, particularly during Christmas and other holidays, and more particularly for the decoration of Christmas trees, and the like. Probably the most popular light sets currently available on the market, and in widespread use, comprise thirty-five or fifty miniature light lamps each, with each lamp typically having an operating voltage rating of 3.5 or 2.5 volts respectively, and whose filaments are connected in an electrical series circuit arrangement.
A string of lights may be made to flash, or turn on and off, by including a flasher light lamp as one of the light lamps of the string. Such a flasher light lamp typically includes a bi-metallic strip which conducts current to the filament. As the bi-metallic strip heats up, it moves away from the filament and breaks the current connection, causing the bulb to turn off. The bi-metallic strip then cools and returns to the initial position, allowing current to flow and begin the on and off cycle again. All of the bulbs in such a light string turn on and off simultaneously, as the lights are connected in series.
The present invention advantageously provides methods and apparatus for an improved series connected light string. In one aspect, the present invention provides a voltage regulated filament shunting circuit for use in connection with a series connected light string of incandescent flasher type light bulbs. Each flasher light is connected in parallel with a silicon type semiconductor shunting device. The shunting device has a predetermined voltage drop value which is slightly greater than the voltage normally applied to said bulbs. The semiconductor shunt becomes more conductive only when the peak voltage applied across the shunt exceeds its predetermined voltage drop value. The predetermined voltage drop for a particular shunt is exceeded whenever its associated flasher lamp opens periodically as it is designed to do or if the flasher lamp becomes inoperable. Such a circuit arrangement provides for the continued flow of current through all of the remaining lamps in the string, together with little apparent change in illumination from any of those lamps remaining operative in the string even though a substantial number of total lamps in the string are simultaneously inoperative or turned off. All but one lamp may be inoperative or off and the sole operative lamp will continue to operate.
The silicon semiconductor shunt of the present invention is designed so that it is always conducting, regardless of whether its associated lamp is xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d. The shunt operates in either of two low impedance states, or in other words, two conducting levels. By operating the silicon semiconductor shunt between two low impedance conducting levels, better voltage regulation is obtained. Effectively, neither of the two low impedance states rises above several hundred ohms. The operation of the shunt in this invention occurs in the steep part of the electrical current-voltage (IV) curve beyond the xe2x80x9ckneexe2x80x9d where the slope rises sharply. Although the light string operates somewhat less efficiently in terms of power consumption when operating in this manner, the increased voltage regulation obtained as a consequence of this operation results in an almost flicker-free operation of the string as lights turn on and off. Visually, the effect is highly appealing.
The two conducting levels of the semiconductor shunt device can be defined as the sustaining level and the lamp filament replacement level. The sustaining level is the higher resistance of the two resistance levels in the silicon semiconductor shunt. The impedance of this level is two to eight times (preferably two to four times) that of the lamp resistance when operating normally. Further, the impedance at this level is selected so that it is not more than about 200 ohms, and preferably not more than about 100 ohms. The lamp filament replacement level is that impedance which closely matches or is slightly greater than the parallel equivalent impedance of the lamp operating in parallel with the shunt device, typically between 12 and 25 ohms.
It is therefore a principal object of the present invention to provide a simple and inexpensive silicon type semiconductor voltage regulator filament shunt, or bypass, for each of a plurality of series connected flasher light bulbs, the filament shunt having a predetermined conductive voltage drop which is only slightly greater than the voltage rating of said bulbs when operating, and the shunt becoming more conductive whenever the peak voltage applied across the shunt exceeds its predetermined voltage drop conductive value. Thus, a continued and uninterrupted flow of current is provided through each of the remaining lamps in the string, together with little apparent change in illumination from the lamps.
While this invention is directed toward tighter voltage regulation, which is desirable for a multi flashing or twinkling light string where all or most all of the lamps are of the flasher type, a light string in accordance with the present invention may comprise all regular (non-flashing) lamps or a combination of regular and flasher lamps as well.
It is another object of the present invention to provide a new series-connected random twinkle light string which has the desirable features of the lamps flashing on and off at various points in time and yet is of very simple and economical construction and is relatively inexpensive to manufacture in mass quantities, thereby keeping the overall cost of manufacturing the final product at a minimum.
It is still another object of the present invention to provide a series-connected light bulb string in which the light emitted from each flashing incandescent light bulb will optionally appear, disappear, and reappear independently and continuously along the entire string, thereby creating a most striking, novel and unusual twinkling effect.
A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following detailed description and the accompanying drawings.